The present disclosure relates to rotary electric machines such as electric motors or generators, particularly of the polyphase type, and, more particularly, to apparatuses and methods for manufacturing multiple-pole stators used therein.
Rotary electric machines operate by exploiting the interaction of rotating magnetic fields with a rotor carrying magnets, the rotor disposed within and rotatable relative to a stator. The rotor is typically fixed to a shaft mounted for rotation centrally by means of bearings in a casing that surrounds the stator. These machines include armatures or a configuration of insulated wire coils in the stator, which are distributed about the stator central axis, the coils arranged in a progressive sequence to define the different phases. The stator coil windings are typically wound around ferromagnetic poles of the stator to enhance the strength of the generated magnetic field. The poles generally are tooth-like cross sections that are usually rectangular or trapezoidal, and typically defined by longitudinal slots in the stator core.
In a polyphase electric motor, flowing current of different phases through a progressive sequence of wire coils in the stator generates rotating magnetic fields in the stator, which impart electromechanical torque to the rotor and its shaft. Conversely, in a polyphase electric generator, externally forced rotation of the shaft and rotor imparts rotation to magnetic fields that induce current flows in the stator coils.
As is well-known in the relevant art, the stator may have a stator core defined by a stack of interlocked, ferrous laminae each having a hole, the holes being aligned in the lamina stack to form a stator core central bore. Thus, the stator core may be a unitary annular member, its central bore defining a stator core radially internal face that is typically cylindrical and centered about a stator central axis. The radially internal face is typically provided with a plurality of generally axially extending elongate slots formed by aligned, notched portions of the laminae holes. The stator slots pass axially through the lamina stack adjacent the central bore since they extend over the entire axial length of the lamina stack and are open radially on an internal side and the two opposite axial ends. The stator slots extend between the axially opposite ends of the stator core and define the stator poles. The slots formed by the lamina stack may lie in planes that intersect along and contain the stator central axis, but are sometimes inclined with respect to that axis. It may nevertheless be said that the stator core slots are generally parallel with the stator central axis. The plurality of stator slots is typically distributed at an even pitch about the stator central axis. Relative to the stator, radial and axial directions mentioned herein are respective to the stator central axis, and the stator slots generally extend radially outwardly from and axially along the stator central axis.
Disposed in and extending along these stator slots are elongate electrical conductors that define the stator coil windings. By virtue of the conductors being routed through the stator slots, they are wrapped about the stator poles. Typically, a stator slot insulator insert is interposed between the conductors and the edges of the stator slots to ensure electrical isolation of the stator coil from the stator core. The insulator insert is inserted into the slot before a conductor is installed therein.
In a polyphase rotary electric machine, the stator coil windings include a plurality of (typically three) different phase windings each consisting of a continuous, elongate electrical conductor, such as a wire or bar. The conductor may, for example, be made from copper covered with an insulator such as enamel. Alternatively, each phase winding may include an interconnected plurality of such conductors. Conventional wire sizes may be used for the conductors of the wire coils. Optionally, thick bar conductors can be used for making a wire coil with a designed current-carrying capacity requiring fewer turns than is possible with smaller size wire. The conductor cross-section is typically circular or rectangular (including square).
The stator slots may have a radial depth that is a multiple of the cross-sectional dimension of the conductor in the slot's radial direction. In an example three-phase stator, two electrical conductor lengths may be housed within each of the stator slots so as to line up in one row in a radial direction. The electrical conductors are arranged in a predetermined winding pattern to form the stator winding. The particular winding patterns of stator windings may vary considerably between different machine designs, and are generally beyond the scope of the present disclosure.
Thus, a stator assembly includes a stator core, a stator winding constituted by a number of electrical conductors disposed inside slots formed in the stator core, and inserted insulators providing electrical insulation between the stator core and the electrical conductors.
For example, in a three-phase machine having eighty-four stator slots, there are three slot groups, one for each phase, each having twenty-eight slots in which are disposed the conductors of a single current phase. The twenty-eight slots of each slot group or current phase, may be distributed about the stator central axis in, for example, seven equal sets of four circumferentially adjacent slots. Such is a typical example that would be well-understood by one of ordinary skill in the relevant art. Further, each of the three phase windings may consist of a single formed conductor, or an interconnected plurality of formed conductors.
Prior to their installation, the stator winding conductors are formed by bending lengths of the elongate conductors into shapes defining elongate straight portions, herein also referred to as conductor axial branches, that are installed into the stator slots. The axial branches of a conductor are serially connected by relatively shorter head branches, which are conductor portions that generally extend tangentially relative to the stator bore. Depending on its number of axial branches, a formed conductor's pair of connection segments may have more than one head branch disposed therebetween. The head branches typically lie outside of the stator slots, and outside of the stator bore, at one or both axial ends of the stator core. These undulating conductors are thus said to be of the “S-type” and “wave-wound” about the stator poles.
The longitudinal ends of each formed conductor are commonly referred to as its connection segments, and are each typically located at a longitudinal end of an axial branch opposite a connected head branch, at an axial end of the stator core, and preferably at a common stator core axial end. Locating the connection segments of a stator winding at a common axial end of the stator core facilitates their being quickly and easily interconnected. The connection segments of a plurality of conductors in the same phase winding may be interconnected prior, or subsequent, to the stator winding conductors being installed in the stator slots. The interconnection of the connection segments of a phase winding may be done directly, such as through a suitable joining process, for example by soldering or a crimped connector; or indirectly such as through a buss bar assembly. Interconnection of conductors via a buss bar assembly is done subsequent to the installation of the windings into the stator core.
The stator core slot openings may have a circumferential width corresponding to the circumferential width of the conductor wire; the opening may have a circumferential width substantially equal to the corresponding cross-sectional dimension of the conductor. Retention of the coil windings in the stator core may be done by deforming the axial branch occupying the radially innermost position to broaden it in a circumferential direction, relative to the stator central axis, at a plurality of discrete locations axially therealong. The deformation of the conductor compresses it against the opposite sides of its stator slot and holds it, and conductor axial branches occupying the other positions, inside the stator slot. Alternatively, once the coil windings have been inserted into the stator slots, insulating covers may be installed over the stator slots to mechanically retain the conductors in position. Alternatively, or additionally, an insulating resin is applied to the assembly of the stator core and the installed windings to connect the conductors together, and to fix the conductors to and insulate them from the stator core.
Insertion of the stator coil windings into the stator core slots may be from a cylindrical magazine, also referred to in the art as a slotted bobbin or dummy rotor, onto which the conductors have been loaded, and which is insertable into the bore of the stator core. Such a magazine, while outside of the stator bore, is loaded with the conductors of the stator windings in an arrangement corresponding to, e.g., generally radially reversed relative to, their desired configurations in the resulting stator. The conductors loaded onto the magazine may be partially or fully preformed as described above, or may be formed on the magazine, which serves as a mandrel as well as a carrier of the formed conductors and an aid to their insertion into the stator core slots. Such magazines are well known in the art; they typically include a cylindrical part having a radially external surface in which is provided a plurality of radial recesses extending in respective radial planes equiangularly distributed around the central axis of the magazine. The magazine recesses also extend between the axially opposite ends of the generally cylindrical magazine. The radial recesses in the magazine are equal in number to the number of slots in the stator.
The magazine, once loaded with formed conductors arranged in a desired winding pattern, has an insertion mode in which the magazine has been disposed within the cylindrical stator core bore, with the magazine recesses aligned with the stator slots in the surrounding, radially inner cylindrical surface of the stator core bore. The radial disposition of the conductor axial branches carried by the magazine recesses, correspond to their radial disposition in the resulting stator assembly. Thus, relative to the magazine, the magazine-to-stator core conductor transference may be described as being according to a last-in-first-out or LIFO system. The magazine has radial blade members moveably disposed in the magazine recesses. The blade members are used to push the arranged, preformed conductors carried by the magazine radially outwardly from the recesses, away from the magazine central axis and towards the stator core bore, and press the axial branches into the stator slots.
A known magazine, winding installation method, and apparatus suitable for insertion of windings into stator slots are described in U.S. Pat. No. 2,873,514, issued Feb. 17, 1959, the disclosure of which is incorporated herein by reference.
Methods and apparatuses that streamline prior stator assembly processes and facilitate greater speed and efficiency thereof would be desirable advancements in the relevant art.